Because of environmental concerns, automobile manufacturers and government regulators have introduced new, more stringent performance requirements for lubricants. As a result, the specifications for finished lubricants are requiring products having excellent low temperature properties, high oxidation stability, and low volatility. Currently, only a small fraction of the base oils manufactured today are able to meet these demanding specifications.
Group II plus base oil, though not an official American Petroleum Institute (API) designation, is a term used to describe API Group II stocks of higher viscosity index (110-119) and lower volatility than comparable Group II stocks.
Due to their low viscosity and low volatility, API Group III base oils have become the base stocks of choice for the next generation of lubricant compositions. This in turn has lead to a greater demand for Group III base oils. However, producing Group III base oils can be difficult requiring the use of special high viscosity index gas oils which can be higher in cost than gas oils used to make Group II base oils. In addition, the production of Group III base oils can also involve hydrocracking gas oils at higher severity in order to get the viscosity index to at least 120 which may result in lower yield, downgrading potential base oil to lower valued diesel and other light products, and shortening the hydrocracker catalyst life.
It would be advantageous if a refiner could simply switch from Group II base oil production to Group II plus or Group III base oil production by adding a minor amount of a different second feed to the hydrocracked Group II base oil ahead of an isomerization dewaxing unit in order to boost the viscosity index for as long as the Group II plus or Group III base oil production was required. It would also be advantageous if the second feed were low in cost and had additional benefits, such as reduction of environmental waste.
One potential low cost feed is waste plastics. According to a 2009 report from the U.S. Environmental Protection Agency Office of Resource Conservation and Recovery, about 52% of all plastic packaging in the United States is composed of polyethylene, the preferred feed for plastics conversion to lubricating oils. Polyethylene plastic is found in two main forms: high-density polyethylene (HDPE), which is used for making rigid containers such as bottles, and low-density polyethylene (LDPE), which is used for making flexible films such as grocery bags. Plastics waste is a fast growing waste product, with about 30 million tons per year generated in 2008 compared to about 18 million tons per year generated in 1995. Transforming waste plastic material and particularly polyethylene into useful products presents a unique opportunity to address a growing environmental problem.
Accordingly, it would be desirable to devise an economical process which converts hydrocracked oils blended with a wax derived from pyrolyzing a plastics feed into Group II plus or Group III base oils.